This invention concerns industrial processes and more particularly metal cutting, such as punching or shearing in which significant sound noise is generated, creating working environmental problems. Sound or noise level is a function of many variables, i.e., material hardness and thickness, punch size, punch shear, impact velocity, punching velocity, and stripping velocity.
Considerable work has been done in this area to alleviate the noise problem in punching operations. See published UK patent application GB 2036923A in which a damping device is used to alleviate noise and vibrations in a punch press as an example.
It has heretofore been proposed to use a hydrauliccylinder coupled to the ram to drive the punch, with feed back control systems employed to provide precise control over punching velocities. See U.S. Pat. No. 4,116,122 for an example of a press using such a control system to improve the quality of the punched part.
In U.S. Pat. No. 4,823,658, controlled ram speed is described as allowing reduced punching noise.
U.S. Pat. No. 4,208,935 describes a feed back control over the punch ram to reduce the exit speed of the punch at the end of the punching process to eliminate noise and strain.
U.S. Pat. Nos. 5,031,431 and 5,027,631 and UK published application GB2186394A describe reducing ram velocities to limit sound or noise in accordance with stored programs which have previously been calculated or empirically determined to keep noise limits within acceptable limits for particular legal limits. In some cases time of shear or ram pressure are relied to correlate with noise level which may or may not hold true in practice.
These approaches require extensive and time consuming testing and compilation of data and elaborate computer programs and stored data libraries to carry out, and actual results may vary from calculated noise levels. Stripping noise is not accounted for.
In the event that the daily average level of noise exposure is limited by legal authorities or that limits are otherwise desirable as to avoid the need for wearing ear protection, the prior control schemes do not provide any means to insure that allowable time averaged noise levels are not exceeded.
In addition, the effects of the operation of nearby machinery or other various factors unique to a particular location are not able to be taken into account.
The object of the present invention is to eliminate the need for theoretical studies or extensive laboratory testing and elaborate computer programs, and to provide a means to insure that time averaged noise levels and or peak level noise are not exceeded.